Water distillation apparatus with vapor trap



Jam 17, 1967 v. c. SMITH ,2

. I WATER DISTILLATIO N APPARATUS WITH VAPOR TRAP Filed Aug. '7, 1963 l 34 BAFFLE a u 1 STiLL COOLER INVENTOR.

VERITY C. SMITH ATTORNEYS United States Patent 3,298,929 WATER DISTILLATION APPARATUS WITH VAPOR TRAP Verity C. Smith, Dedham, Mass., assignor to Barnstead Still & Sterilizer Co., Boston, Mass., a corporation of Massachusetts Filed Aug. 7,1963, Ser. No. 300,474 1 Claim. (Cl. 202190) This invention relates to water distillation, and in particular to apparatus for obtaining a distillate of high purity from the base of a countercurrent vapor-distillate unit in a water distillation system.

High purity water distillation systems frequently include a couriter'current vapor-distillate .unit, called a scrubbing column, between the still and the condenser. The vapors and distillate flow through the scrubbing column in intimate countercurrent contact with one another, thevapor reheating the distillate substantially to the vaporization temperature and removing from the distillate the last trace of dissolved gases, which are vented from the top of the column. In practice, countercurrent scrubbing of the distillate with the vapor will frequently. result in an increase in resistivity of the distillate, the normal method ofmeasuring its purity, from a value of less than 500,000 ohm-centimeters to a value of greater than 3,000,000 ohm-centimeters.

The distillate collects in the bottom of the scrubbing column, and is fed through a cooler to a storage tank, which may be combined with the cooler. It has been found in some instances that the purity of the distillate drawn from the storage tank is quite low. Since tests of the distillate purity showed the distillate supplied to the cooler to be of the normal high purity, but the distillate yield flowing from the cooler to be of a low purity, the cooler was thought to be defective. Replacement of the cooler usually resulted in a return of the distillate yield to a high purity level for a while, after which the purity of the distillate yield would drop back to a low purity level. This exceedingly troublesome fluctuation in the purity of the distillate yield rendered the high purity distillation system unreliable. Because of this, the purity of the distillate could not be assured by the system itself, but could only be assured by periodically testing the distillate yield. 3

The present invention overcomes these problems, and provides a high purity distillation system which reliably and consistently yields a high purity distillate.

The present invention is predicated on the assumption that impurity vapors also collect in-the bottom. of the scrubbing column and are fed with the distillate to the cooler and storage unit. When distillate withdrawn from the outlet of the scrubbing column is tested for purity, these vapors are naturally vented from the distillate as it is withdrawn, and the test shows the distillate to be of a high purity. However, when fed to the cooler, these impurity vapors condense as the distillate is cooled, contaminating the distillate yield. The presence of these impurity vapors has notbeen detected by analytical procedures. Yet, their presence is indicated by the discovery that when a vapor trap is included between the scrubbing column and the cooler, the cooler reliably and consistently yields a high purity distillate. For example, by installing a vapor trap at the outlet of the scrubbing column of a high purity distillation system yielding a low purity distillate, the purity of the distillate flowing from the cooler will increase from a level of 300,000 ohmcentimeters to a level of 3,000,000 ohm-centimeters within an hour after installation of the vapor trap, and the purity will remain at this high level.

' reference to the ice The vapor trap of the present invention receives the reheated distillate output from the scrubbing column and permits only the liquid distillate to flow therethrough. Preferably, the vapor trapincludes a housing divided into two compartments only in liquid communication with one another so that only the high purity distillate can flow into the downstream compartment, the impurity vapors collecting in the upstream compartment being vented to the atmosphere.

The invention s further described in detail below with :ompanying drawings, in which: :ally illustrates the distillation system of the present ntion with the condenser and scrubbing column shc... in vertical cross-section, a vapor trap being included between the distillate outlet of the scrubbing column and the-cooler; and

FIG. 2 is a vertical cross-sectional view of the vapor trap in operation.

A typical water distillation system incorporating the vapor trap is shown in FIG. 1 and includes a still 1, a baflle 2 and a chamber 3 housing the condenser and scrubbing column, connected in serial fluid communication with one another by conduits 4 and 5. Each of these components of the distillation system may be of conventional design, and form of themselves no part of this invention.

The still 1 receives the water to be distilled and includes heating means for converting the water to vapor. The vapor passes upwardly through conduit 4, baflle 2, conduit 5, the scrubbing column 6 within chamber 3 to the coils of condenser 7. The vapors are condensed to a liquid distillate by condenser 7, and the distillate drops from the condensing coils back through the packing material of the scrubbing column in intimate contact with the upwardly flowing vapors. During this countercurrent flow of the vapors and distillate, the distillate is heated by the vapors and the last trace of dissolved gases are scrubbed from the distillate to purify it. The gases rising to the top of the chamber are vented by a vent cap in the top wall of the chamber.

The hot liquid distillate collects in the bottom of the scrubbing column, and flows through conduit 8 to a vapor trap 9. The vapor trap blocks the flow past the trap of any vapors flowing with the distillate from the scrubbing column, and vents these vapors to the atmosphere. The purified distillate flows from the vapor trap through an outlet conduit 11 to a cooler12, which also may store the purified distillate for use. While the vapor trap is shown as a separate unit, it nia'y be formed within and as a portion of chamber 3, or even as a portion of the cooler.

A presently preferred construction of the vapor trap 9 is illustrated in FIG. 2. The vapor trap includes a cylindrical housing or casing 13 comprising a base pan 14, a cylindrical side wall 15, and a top wall 16 receiving the outer marginal portions of one another and soldered, brazed, or otherwise sealed and attached to one another at the overlapping marginal portions. An inlet opening 17 is provided in the side wall 15 adjacent the top wall 16, and an interiorly threaded inlet nipple 18 which receives the threaded end of conduit 8 is secured and sealed about the outer peripherial portion of the side wall 15 defining the inlet opening. An outlet opening 21 is provided in the side wall 15 opposite and lower than the inlet opening 17, and an interiorly threaded outlet nipple 22 which receives the threaded end of conduit 11 is secured and sealed about the outer peripheral portion of side wall 15 defining the outlet opening.

A baflie 23 is secured and sealed within the cylindrical canister 13 to the side wall 15 about outlet opening 21. The baffle includes a top wall shaped as a segment on a chord of the cylindrical canister and a rectangular side FIG. 1 scherr wall, which walls are sealed to one another and to the side wall of the canister. The lower side wall end of the baflle is spaced from the base pan 14 to permit fluid to flow from the inlet under the bafile to the outlet. The baflle isolates the cylindrical canister into an inlet compartment 24 and an outlet compartment 25.

During operation, the hot liquid distillate collects in the bottom of the scrubbing column 6 with any vapor impurities and flows through conduit 8 to the inlet compartment 24 of the vapor trap 9. The liquid distillate collects in the lower portion of the inlet compartment, and any vapor impurities flowing with the distillate collect in the top portion of the inlet compartment. The liquid distillate flows from the inlet compartment under the side wall of the bafile 23 to the outlet compartment 25, filling it to the level of outlet opening 21. The baffle wall extends well into the distillate pool in the vapor trap, and positively separates and isolates the vapor impurities collecting in the top portion of the inlet compartment from the outlet compartment. Thus, only the pure distillate flows from the outlet compartment 25 through conduit 11 to the cooler 12.

The top wall 16 of the vapor trap includes vapor vent opening 26 through which the vapor collecting in the top portion of the first compartment may be vented to the atmosphere. A flapper valve 27 is attached to the top wall over the vapor vents. Under a slight vapor pressure, such as normally exists in the scrubbing column, the outer rim portion of the head of the flapper valve will lift from the top wall, as shown in FIG. 2, to vent vapors collecting within the top portion of the inlet compartment to the atmosphere. Preferably top wall 16 is convex, and slopes away from vents 26 to positively cause water condensing on the exterior surface of the top wall to flow outwardly, rather than back through the vents and into the vapor trap.

A dust cover 31 is secured over the cylindrical casing spaced from the top wall in any convenient manner, as by machine screws 32 passed through openings adjacent the rim of the cover and threadably received in studs 33 welded or otherwise attached to the top wall. The dust cover and the top wall form a tortuous path for vapors flowing from the vents outwardly under the rim of the cover to the atmosphere, and this tortuous path impedes any countercurrent flow of impurities from the atmosphere back into the vapor trap. While a more elaborate venting arrangement may be provided if desired, such as a filter valved to permit vapors to flow only from the vapor trap, the illustrated venting arrangement has proven entirely adequate. The center portion of base pan 14 preferably is depressed, and receives the inlet of a drain cock 34 through which the distillate may be drained from the interior of the vapor vent when desired.

Preferably the members forming the distillation systern, including the vapor trap and the cooler, are completely tinned on the inside surfaces exposed to the vapors and distillate, as is common. The vapor trap may be formed as a part of the scrubbing column, or as a part of the cooler if so desired. The vapor trap need not necessarily vent the vapors to the atmospheric, but may only block the flow of the vapors to the cooler.

While the preferred construction of the vapor trap has been described, it will be apparent that any conventional vapor trap may be employed to permit only the distillate to flow to the cooler. Also, while a scrubbing column generally similar to that disclosed in my US. Patent 2,816,064 issued December 10, 1957 for Water Distillation is shown, the vapor trap may be employed with various other countercurrent vapor-distillate units, such as the unit disclosed in my US. patent application, Serial No. 269,503 filed April 1, 1963, for Water Distillation Condenser, or even in other distillation systems in which the distillate is reheated to drive off dissolved gases. In short, various modifications of the disclosed system will be apparent to those skilled in the art and familiar with the principles herein disclosed, and such modifications may be made without departing from the spirit and scope of the invention.

I claim:

In a water distillation system which includes in vertical alignment a still, a vented condenser, and a scrubbing column between the still and condenser having a distillate outlet at the bottom of said scrubbing column, the improvement comprising a vapor trap housing, a baffle wall within the housing dividing the housing into an inlet compartment and an outlet compartment in fluid communication with one another only adjacent the base of the housing, means for supplying the distillate collected at the outlet of the scrubbing column to the inlet compartment, the distillate collecting in the lower portion of the inlet compartment and flowing to the outlet compartment, means for venting the upper portion of the inlet compartment, a dust cover overlying said venting means,

and means at the outlet compartment for supplying the distillate collecting in the outlet compartment to a cooler and storage unit.

References Cited by the Examiner UNITED STATES PATENTS 233,184 10/1880 Baird 203--10 424,124 3/ 1890 Moore 202202 X 520,525 5/1894 Havenstrite 20310 1,966,938 7/1934 Stone 202-10 2,816,064 12/1957 Smith 203l0 NORMAN YUDKOFF, Primary Examiner. F. E. DRUMMOND, Assistant Examiner. 

